Depth Limiting Drill

ABSTRACT

A depth limiting device for a drill includes a main body, an axial braking structure, and a limited shrinking structure. The axial braking structure is attached to the main body. The limited shrinking structure surrounds a drill rod of the drill, is slidably attached to the main body, and is in a home position or a compressed position. The axial braking structure axially brakes the drill rod such that the drill rod moves together with the depth limiting device. When the drill rod enters into a subject, the limited shrinking structure is pressed against the subject, moves from the home position to the compressed position, and stops the drill rod from entering further into the subject.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a depth limiting device used for adrill and a drill that includes the depth limiting device.

Discussion of the Related Art

A drill is a tool used for drilling a hole in a subject. For example, abone drill can be used for drilling a hole in a bone in a surgery. Whena drill is used for drilling a hole in a bone, a surgical doctor holdsthe drill and pressurizes for drilling. After the drill breaks throughthe bone substance completely, the electric drill falls through, and itis often difficult and even sometime impossible for the surgical doctorto stop pressurizing at the same time, so the drill may drill forwardscontinuously. In the drilling process, damages of tissues may beresulted; and if vessels and nerves existing in the heading direction ofthe drill are damaged, serious consequences may be resulted. Inaddition, measurement of the depth of the drilling hole is also neededfor determination of a suitable screw after the hole drilling process isfinished. Existing drills, however, only have a hole drilling function,so the surgical doctor needs to measure the drilling hole by inserting adepth measuring device in the drilled hole. There is a need for improveddrill that will reduce the damages to tissues, vessels, and nervesduring the drilling process.

SUMMARY OF THE INVENTION

According to one embodiment, there is provided a depth limiting devicefor a drill that includes a main body; an axial braking structure, theaxial braking structure being attached to the main body; and a limitedshrinking structure, the limited shrinking structure surrounding a drillrod of the drill, being slidably attached to the main body, and being ina home position or a compressed position. The axial braking structureaxially brakes the drill rod such that the drill rod moves together withthe depth limiting device. When the drill rod enters into a subject, thelimited shrinking structure is pressed against the subject, moves fromthe home position to the compressed position, and stops the drill rodfrom entering further into the subject.

In another embodiment, the limited shrinking structure includes aconnecting sleeve, a drill rod bushing, and a first spring; the drillrod bushing houses the drill rod and slides relative to the drill rod;the connecting sleeve includes a retraction space therein and the firstspring is located in the retraction space.

In another embodiment, the axial braking structure comprises a pluralityof grooves adapted for axially braking the drill rod, a structure with abulge which can be clamped in each groove, and an operating part for thestructure with the bulge.

In another embodiment, the axial braking structure further includes anaxial braking block and a second spring. A hole is formed in the axialbraking block, the structure with the bulge is formed at an inner wallof the hole, the drill rod passes through the hole, the plurality ofgrooves are formed on the drill rod, the axial braking block is locatedinside the main body, the axial braking block has a compression fittingsurface adapted for lifting the axial braking block and an opposite sideof the compression fitting surface, and a cavity is formed between theopposite side and the main body. The second spring is located in thecavity.

In another embodiment, the axial braking structure further includes atrigger, a limiting rod, and a third spring. The trigger includes ahand-held section and a horizontal section, the horizontal section isvertical to the hand-held section, the horizontal section of the triggeris vertical to the axial braking block, a front end of the horizontalsection of the trigger connects with the compression fitting surface.The limiting rod connects with one end of the horizontal section of thetrigger and the compression fitting surface. The third spring is locatedbetween another end of the horizontal section of the trigger and themain body, and the another end of the horizontal section of the triggeris supported at the main body.

In another embodiment, the main body includes a handle and a protectiveplate. The protective plate connects with the handle and protecting thetrigger.

In another embodiment, the main body further includes a front part and arear part. The rear part surrounds the axial braking block, the frontpart supports the trigger, the connecting sleeve and the first springare located inside the rear part, a front end of the drill rod bushingis attached to the front part, and a rear end of the drill rod bushingis slidably attached to the connecting sleeve.

In another embodiment, the axial braking structure includes a frictionbraking structure for the drill rod and an operating part for thefriction braking structure.

In another embodiment, the friction braking structure includes an outertaper sleeve, an inner taper sleeve, a sixth spring, a trigger, and aU-shaped connecting rod. The outer taper sleeve surrounds the drill rod,the inner taper sleeve surrounds the outer taper sleeve and is attachedinside the main body, an outer surface of the outer taper sleeve and aninner surface of the inner taper sleeve are in a friction fit, anexpansion space is formed inside the inner taper sleeve, the sixthspring is located in the expansion space, a bottom of the U-shapedconnecting rod connects with the trigger, two ends of the U-shapedconnecting rod connects with two rollers, and the two rollers drive theouter taper sleeve towards the inner taper sleeve along the drill rod.

In another embodiment, the depth limiting device further includes ahandle. The handle is parallel to the trigger and attached to the rearend of the main body, and the connecting sleeve is attached to the frontend of the main body.

In another embodiment, the main body includes a protective sleeve, asheath, a sleeve cylinder, and a seventh spring. The protective sleevesurrounds the drill rod, the sheath surrounds the protective sleeve, thesleeve cylinder is attached to drill rod, a rear end of the sheathconnects with a front end of the sleeve cylinder, a rear end of theprotective sleeve is located inside the sheath and slidably connectswith the sheath, a front end of the protective sleeve connects with theconnecting sleeve, and the seventh spring is located between theconnecting sleeve and the sheath.

In another embodiment, the depth limiting device further includes aguide block and a limiting pin. The rear end of the protective sleeveprotects the guide block which can slide along the inner wall of thesheath, and the limiting pin is located on the rear end of the sheathand brakes the guide block.

In another embodiment, the depth limiting device further includes abraking ring, a second connecting rod, and a trigger. The braking ringis located on the protective sleeve and within the sheath, the brakingring connects with the trigger via the second connecting rod, gaps existbetween the inner wall of the breaking ring and the outer wall of theprotective sleeve and between the outer wall of the braking ring and theinner wall of the sheath, a wall thickness center of the braking ring iscoincided with a center of a gap between the protective sleeve and thesheath, and a rear end of the second connecting rod is supported at themain body.

In another embodiment, the depth limiting device further includes asecond locking block, a steel sheet spring, a trigger, and a thirdconnecting rod. The second lock block is rotationally attached to thesheath, the steel sheet spring is adapted for returning the secondlocking block to an original position, one end of the second lockingblock touches the periphery of a back section of the protective sleeve,another end of the second locking block connects with the triggerthrough the third connecting rod, and a rear end of the third connectingrod is supported at the main body.

In another embodiment, a drill includes the depth limiting devicedescribed above.

In yet another embodiment, there is provided a depth limiting device fora drill. The depth limiting device includes includes a main body; alocking shaft, the locking shaft having a plurality of grooves; a firstlocking block, one end of the first locking block having a bulge; alinear motion cam, the linear motion cam connecting with another end ofthe first blocking block; a rotary motion cam, the rotary motion camconnecting with the linear motion cam; a guide sleeve, the guide sleevebeing located at outside of the first locking block, a retraction spacebeing formed between the guide sleeve and the linear motion cam, and aforth spring being located in the retraction space; a first connectingrod, an end of the first connecting rod connecting with a drill rod ofthe drill; and a connecting sleeve, the connecting sleeve being locatedat a front end of the locking shaft and slidably connecting with anotherend of the first connecting rod. A rear end of the locking shaft and themain body form an expansion space, and a fifth spring is located in theexpansion space.

In another embodiment, the main body is attached to a drill via abracket.

In another embodiment, a drill includes the depth limiting devicedescribed above.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 shows a limited shrinking structure.

FIG. 2 is a side view of the depth limiting device of Example 1;

FIG. 3 is a partial enlarged drawing of FIG. 1;

FIG. 4 is a side view of the depth limiting device of Example 2;

FIG. 5 is a top view of the depth limiting device shown in FIG. 3;

FIG. 6 is a cross-sectional view taken through A in FIG. 3;

FIG. 7 is a side view of the depth limiting device of Example 3;

FIG. 8 is a cross-sectional view taken through A-A sectional in FIG. 6;

FIG. 9 is a partial enlarged drawing of FIG. 6;

FIG. 10 is a side of the depth limiting device of Example 4;

FIG. 11 is a partial enlarged drawing of FIG. 9;

FIG. 12 is a side view of the depth limiting device of Example 5;

FIG. 13 is a partial enlarged drawing of FIG. 11; and

FIG. 14 shows the schematic diagram of the limited shrinking structureof Example 4 and Example 5.

In the Figures, the reference numerals have the followings designations:

1—drill rod, 2—drill rod bushing, 3—connecting sleeve, 4—retractionspace, 5—first spring, 6—axial braking block, 7—cavity, 8—second spring,9—trigger, 9.1—hand—held section, 9.2—horizontal section, 10—compressionfitting surface, 11—limiting rod, 12—third spring, 13—handle,14—protective plate, 15—main body, 15.1—front part, 15.2—rear part,16—locking shaft, 17—first locking block, 18—linear motion cam,19—rotary motion cam, 20—guide sleeve, 21—forth spring, 22—firstconnecting rod, 23—fifth spring, 24—bracket, 25—electric drill, 26—outertaper sleeve, 27—inner taper sleeve, 28—sixth spring, 29—U—shapedconnecting rod, 30—roller, 31—protective sleeve, 32—sheath, 33—sleevecylinder, 34—guide block, 35—limiting pin, 36—braking ring, 37—secondconnecting rod, 38—second locking block, 39—third connecting rod,40—seventh spring, 100—subject, 101—limited shrinking structure, and102—axial braking structure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The depth limiting device used for a drill of the present invention isfurther described in detail by combining with the accompanying drawings.

The depth limiting device used for a drill includes a main body; anaxial braking structure, braking the drill rod axially at any time; anda limited shrinking structure capable of sliding relative to a drill rodof the drill, realizing limited extension of the drill rod. The axialbraking structure is attached to the main body.

The limited shrinking structure surrounds a drill rod of the drill, isslidably attached to main body, and can be in a home position or acompressed position. FIG. 1A and FIG. 1B show a limited shrinkingstructure 101 in a home position where first spring 5 pushes drill rodbushing 2 forward against the front end of connecting sleeve 3. Firstspring 5 is located in retraction space 4. Other structures that have asame function as first spring 5 can be used instead of first spring 5.FIG. 1C shows that the limited shrinking structure 101 in a compressedposition. Specifically, the axial braking structure axially brakes drillrod 1 such that the drill rod 1 moves together with the depth limitingdevice. When drill rod 1 enters into a subject 100, drill rod bushing 2is pressed against the subject 100, moves from the home position to thecompressed position, and stops the drill rod from entering further intothe subject 100. Distance ‘d” is the distance that drill rod bushing 2moves from the home position to the compression, and it is also thedepth limit of the depth limiting device. After the drilling iscomplete, first spring 5 pushes drill rod bushing 2 back to the homeposition.

The axial braking structure includes a plurality of groove structurescapable of axially braking the drill rod, a structure with a bulge whichcan be clamped in each groove and an operating part of the structure.Alternatively, the axial braking structure includes a friction brakingstructure that results in friction braking for the drill rod and anoperating part of the friction braking structure.

The depth limiting device is further illustrated in the followingexamples.

Example 1: as shown in the FIGS. 2 and 3, axial braking structure 102includes an axial braking block; a through hole that is formed in theaxial braking block; a drill rod with multiple grooves in the same shapethat penetrates the through hole; and a bulge which can be clamped intoeach groove that is formed at the inner wall of the through hole. Theaxial braking block is located in the main body, and has a compressionfitting surface adapted for lifting the axial braking block and anopposite side of the compression fitting surface. A cavity is formedbetween the opposite side and the main body, and a second spring (resetspring) of the axial braking block is arranged in the cavity. The axialbraking structure further includes a trigger. The trigger includes ahand-held section and a horizontal section which is vertical to thehand-held section; the horizontal section of the trigger is vertical tothe axial braking block. The compression fitting surface is arrangedbetween the front end of the horizontal section of the trigger and thebottom of the axial braking block; the main body is provided with alimiting rod with the position thereof corresponding to one end of thehorizontal section of the trigger where the compression fitting surfaceis arranged; the other end of the horizontal section of the trigger issupported at the main body; and a third spring (reset spring) isarranged between the other end of the horizontal section of the triggerand the main body. The main body includes a front part and a rear part;the rear part is arranged outside the axial braking block; the triggeris supported at the front part; the connecting sleeve and the firstspring of the limited shrinking structure are arranged at the rear part;the drill rod bushing which is arranged on the drill rod in a sleevingmanner is arranged at the front part of the main body in a penetratingmanner and is fixedly connected with the front part; the end part of therear end of the drill rod bushing is connected in the connecting sleevein the sliding manner; retraction space of the drill rod bushing remainsin the connecting sleeve, and the first spring is arranged in theretraction space.

Example 2: as shown in the FIGS. 4, 5 and 6, the axial braking structureincludes a locking shaft, the groove structures being formed in thelocking shaft; a structure with a bulge which can be clamped in eachgroove, the structure being a first locking block, the bulge beingarranged at one end of the first locking block while the other end ofthe first locking block is connected with a linear motion cam; a rotarymotion cam which matches the linear motion cam is connected with atrigger; a guide sleeve which is located at the outside of the firstlocking block is arranged at the position corresponding to the firstlocking block of the main body; expansion space of the first lockingblock being arranged between the guide sleeve and a cam base; a springbeing arranged in the expansion space; the main body corresponding tothe front end of the locking shaft is provided with a connecting sleeve;a first connecting rod being connected in the connecting sleeve in thesliding manner; the connecting sleeve internally including retractionspace of the first connecting rod; a spring being arranged in theretraction spring; the other end of the connecting rod being arranged atthe outside of the drilling rod in a sleeving manner to form thedrilling rod bushing; expansion space existing between the rear end ofthe locking shaft and the main body; and a fifth spring being arrangedin the expansion space. The main body is fixedly arranged on an electricdrill through a bracket.

Example 3: as shown in the FIGS. 7, 8, and 9, the structure whichresults in friction braking for the drill rod is an outer taper sleevearranged on the drill rod in a sleeving manner; an inner taper sleeve isarranged outside the outer taper sleeve; the inner conical surface andthe outer conical surface of the inner and outer taper sleeves are in afriction fit; the inner taper sleeve is arranged in the main body;expansion space remains between the end face of one end of the innertaper sleeve and the end face of the inner taper sleeve, and the endface of the one end of the inner taper sleeve is located within theouter taper sleeve; a spring is connected between the expansion spaceand the main body; the structure for resulting in friction between theouter taper sleeve and the drill rod includes a trigger; the trigger isconnected with the bottom of a U-shaped connecting rod; the two endparts of the U-shaped connecting rod are respectively connected with aroller; and the rollers drive the outer taper sleeve to realize internalmotion of the outer taper sleeve towards the inner taper sleeve alongthe axial line of the drill rod. The connecting sleeve is arranged atthe front end of the main body; and a handle basically parallel with thetrigger is arranged at the rear end of the main body.

Example 4: as shown in the FIGS. 10, 11 and 14, the main body includes aprotective sleeve at the outside of the drill rod, a sheath at theoutside of the protective sleeve and a sleeve cylinder fixedly arrangedon the drill; the rear end of the sheath is fixedly arranged at thefront end of the sleeve cylinder; the rear end of the protective sleeveis arranged in the sheath and is connected with the sheath in thesliding manner; the limited shrinking structure is arranged at the frontend of the protective sleeve, that is to say, the front end of theprotective sleeve is the connecting sleeve fixedly connected with theprotective sleeve; the front end of the connecting sleeve is the drillrod bushing; retraction space exists between the drill rod bushing andthe protective sleeve; the first spring is arranged in the retractionspace; and a seventh spring is arranged at the outside of the protectivesleeve and between the connecting sleeve and the sheath.

The tail end of the protective sleeve protects a guide block which canslide along the inner wall of the sheath; the sheath in front of theguide block and at the back of the braking device is provided with alimiting pin; and the limiting pin is the limiting mechanism of theguide block. The component which results in friction braking for thedrill rod is a braking ring; the braking ring is arranged on theprotective sleeve in a sleeving manner and is arranged within thesheath; the braking ring is connected with the trigger through a secondconnecting rod; a gap remains respectively between the inner wall of thebreaking ring and the outer wall of the protective sleeve and betweenthe outer wall of the braking ring and the inner wall of the sheath; thewall thickness center of the braking ring is coincided with the centerof the gap between the protective sleeve and the sheath; and the tailend of the second connecting rod is supported at the main body.

Example 5: as shown in the FIGS. 12, 13 and 14, the main body includes aprotective sleeve at the outside of the drill rod, a sheath at theoutside of the protective sleeve and a sleeve cylinder fixedly arrangedon the drill; the rear end of the sheath is fixedly arranged at thefront end of the sleeve cylinder; the rear end of the protective sleeveis arranged in the sheath and is connected with the sheath in thesliding manner; the limited shrinking structure is arranged at the frontend of the protective sleeve, that is to say, the front end of theprotective sleeve is the connecting sleeve fixedly connected with theprotective sleeve; the front end of the connecting sleeve is the drillrod bushing; retraction space exists between the drill rod bushing andthe protective sleeve; the first spring is arranged in the retractionspace; and the seventh spring is arranged at the outside of theprotective sleeve and between the connecting sleeve and the sheath. Thetail end of the protective sleeve protects a guide block which can slidealong the inner wall of the sheath; the sheath in front of the guideblock and at the back of the braking device is provided with a limitingpin; and the limiting pin is the limiting mechanism of the guide block.The component which results in friction braking for the drill rod is asecond locking block; the second locking block is rotationally arrangedat the sheath; the second locking block is provided with a steel sheetspring which is capable of restoring the second locking block; one endof the second locking block can be supported on the periphery of theback section of the protective sleeve; the other end of the secondlocking block is connected with the trigger through a third connectingrod; and the tail end of the third connecting rod is supported at themain body.

In addition, each example can be equipped with a depth measurementmechanism, and the form of the depth measurement mechanism can beobtained by one of ordinary skill in the art. The limited shrinkingstructure also can adopt a double-acting pneumatic cylinder structure. Abuffer can be arranged at the terminal of the double-acting pneumaticcylinder structure, so that the limited shrinking structure can reducethe terminal velocity of the pneumatic cylinder steadily and prevent astroke terminal from generating hard impact.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A depth limiting device for a drill, comprising:a main body; an axial braking structure, the axial braking structurebeing attached to the main body; and a limited shrinking structure, thelimited shrinking structure surrounding a drill rod of the drill, beingslidably attached to the main body, and being in a home position or acompressed position, wherein the axial braking structure axially brakesthe drill rod such that the drill rod moves together with the depthlimiting device, and wherein when the drill rod enters into a subject,the limited shrinking structure is pressed against the subject, movesfrom the home position to the compressed position, and stops the drillrod from entering further into the subject.
 2. The depth limiting deviceof claim 1, wherein the limited shrinking structure comprises aconnecting sleeve, a drill rod bushing, and a first spring; the drillrod bushing houses the drill rod and slides relative to the drill rod;the connecting sleeve includes a retraction space therein and the firstspring is located in the retraction space.
 3. The depth limiting deviceof claim 2, wherein the axial braking structure comprises a plurality ofgrooves adapted for axially braking the drill rod, a structure with abulge which can be clamped in each groove, and an operating part for thestructure with the bulge.
 4. The depth limiting device of claim 3,wherein the axial braking structure further comprises: an axial brakingblock, a hole being formed in the axial braking block, the structurewith the bulge being formed at an inner wall of the hole, the drill rodpassing through the hole, the plurality of grooves being formed on thedrill rod, the axial braking block being located inside the main body,the axial braking block having a compression fitting surface adapted forlifting the axial braking block and an opposite side of the compressionfitting surface, and a cavity being formed between the opposite side andthe main body; and a second spring, the second spring being located inthe cavity.
 5. The depth limiting device of claim 4, wherein the axialbraking structure further comprises: a trigger, the trigger including ahand-held section and a horizontal section, the horizontal section beingvertical to the hand-held section, the horizontal section of the triggerbeing vertical to the axial braking block, a front end of the horizontalsection of the trigger connecting with the compression fitting surface;a limiting rod, the limiting rod connecting with one end of thehorizontal section of the trigger and the compression fitting surface;and a third spring, the third spring being located between another endof the horizontal section of the trigger and the main body, the anotherend of the horizontal section of the trigger being supported at the mainbody.
 6. The depth limiting device of claim 5, wherein the main bodycomprises a handle and a protective plate, the protective plateconnecting with the handle and protecting the trigger.
 7. The depthlimiting device of claim 6, wherein the main body further comprises afront part and a rear part, the rear part surrounding the axial brakingblock, the front part supporting the trigger, the connecting sleeve andthe first spring being located inside the rear part, a front end of thedrill rod bushing being attached to the front part, and a rear end ofthe drill rod bushing being slidably attached to the connecting sleeve.8. The depth limiting device of claim 2, wherein the axial brakingstructure comprises a friction braking structure for the drill rod andan operating part for the friction braking structure.
 9. The depthlimiting device of claim 8, wherein the friction braking structurecomprises an outer taper sleeve, an inner taper sleeve, a sixth spring,a trigger, and a U-shaped connecting rod; the outer taper sleevesurrounding the drill rod, the inner taper sleeve surrounding the outertaper sleeve and being attached inside the main body, an outer surfaceof the outer taper sleeve and an inner surface of the inner taper sleevebeing in a friction fit, an expansion space being formed inside theinner taper sleeve, the sixth spring being located in the expansionspace, a bottom of the U-shaped connecting rod connecting with thetrigger, two ends of the U-shaped connecting rod connecting with tworollers, and the two rollers driving the outer taper sleeve towards theinner taper sleeve along the drill rod.
 10. The depth limiting device ofclaim 9, further comprising a handle, wherein the handle is parallel tothe trigger and attached to the rear end of the main body, and theconnecting sleeve is attached to the front end of the main body.
 11. Thedepth limiting device of claim 8, wherein the main body comprises aprotective sleeve, a sheath, a sleeve cylinder, and a seventh spring;the protective sleeve surrounding the drill rod, the sheath surroundingthe protective sleeve, the sleeve cylinder being attached to drill rod,a rear end of the sheath connecting with a front end of the sleevecylinder, a rear end of the protective sleeve being located inside thesheath and slidably connecting with the sheath, a front end of theprotective sleeve connecting with the connecting sleeve, and the seventhspring being located between the connecting sleeve and the sheath. 12.The depth limiting device of claim 11, further comprising a guide blockand a limiting pin, wherein the rear end of the protective sleeveprotects the guide block which can slide along the inner wall of thesheath, and the limiting pin is located on the rear end of the sheathand brakes the guide block.
 13. The depth limiting device of claim 11,further comprising a braking ring, a second connecting rod, and atrigger; wherein the braking ring is located on the protective sleeveand within the sheath, the braking ring connects with the trigger viathe second connecting rod, gaps exist between the inner wall of thebreaking ring and the outer wall of the protective sleeve and betweenthe outer wall of the braking ring and the inner wall of the sheath, awall thickness center of the braking ring is coincided with a center ofa gap between the protective sleeve and the sheath, and a rear end ofthe second connecting rod is supported at the main body.
 14. The depthlimiting device of claim 11, further comprising a second locking block,a steel sheet spring, a trigger, and a third connecting rod; wherein thesecond lock block is rotationally attached to the sheath, the steelsheet spring is adapted for returning the second locking block to anoriginal position, one end of the second locking block touches theperiphery of a back section of the protective sleeve, another end of thesecond locking block connects with the trigger through the thirdconnecting rod, and a rear end of the third connecting rod is supportedat the main body.
 15. The depth limiting device of claim 3, furthercomprising: a first connecting rod, an end of the first connecting rodconnecting with the drill bushing, wherein the axial braking structurecomprises: a locking shaft, the locking shaft having a plurality ofgrooves; a first locking block, one end of the first locking blockhaving a bulge; a linear motion cam, the linear motion cam connectingwith another end of the first blocking block; a rotary motion cam, therotary motion cam connecting with the linear motion cam; a guide sleeve,the guide sleeve being located at outside of the first locking block, aretraction space being formed between the guide sleeve and the linearmotion cam, and a forth spring being located in the retraction space;wherein a rear end of the locking shaft and the main body form anexpansion space, and a fifth spring is located in the expansion space,and wherein the connecting sleeve is located at a front end of thelocking shaft and slidably connecting with another end of the firstconnecting rod.
 16. The depth limiting device of claim 15, wherein themain body is attached to a drill via a bracket.
 17. A drill comprisingthe depth limiting device of claim 1.